1. Field of the Invention
The present invention is directed to a system for inputting three-dimensional (3-D) coordinates for a three-dimensional model and, more particularly, to a system that uses planar motion of an input device to input a pair of orthogonal coordinates and tilt of the input device to input a third (and optionally a fourth) coordinate, orthogonal to each of the coordinates input via the planar motion, to thereby allow a cursor to be moved about within the three-dimensional model.
2. Description of the Related Art
Input devices for controlling a cursor of a three dimensional model generally fall into three categories. The first is the conventional mouse.
The ubiquitous 2-D mouse is currently the input device of choice for desktop 3-D applications for several key reasons including the fact that the mouse operates on a flat horizontal surface. This is less fatiguing when compared with devices which are manipulated and held in 3-D space. The user is not limited to a particular grip. The mouse can be used in a variety of "lazy/relaxed" grips ranging from a precision grip for accurate movements to also simply hitting it to move the cursor from one window to another. The mouse is a relative device with implicit clutching (the act of placing the input device in an active input mode or engaging the input action of the input device), the amount of movement required can be very small. This allows users to be lazy (which is a good thing!). The mouse usually uses position control instead of rate control. This is critical for pointing tasks because it permits ballistic movements and reversible actions (e.g., spin the world around and return back to original position) with predictable response, unlike force-sensing rate controlled devices. The mouse is usually in a stable state where it is ready to be used and does not have to be "disturbed" to park or unpark the device. In contrast, a stylus device will be disturbed when a user picks up or releases it. Since the movement of the buttons are orthogonal to the sensing dimensions, it is easy to operate the buttons without affecting the sensing dimensions (i.e., inadvertently moving the cursor while hitting buttons). The mapping of 2-D mouse device motion to cursor motion is "natural" (i.e., move the mouse up, the cursor moves up; move mouse left, the cursor moves left). This reduces the cognitive load on the user. The implicit clutching mechanism (lifting the device off and replacing it on the work surface) is easily understood and executed, flexible and comfortable when compared to using an explicit clutch button. While these factors make the mouse close to a perfect 2-D input device, it does not inherently support 3-D operations thus requiring the use of graphical manipulators, hotkeys and other extensions to perform 3-D actions. This usually reduces what is often a single integral action into two or more separated, 2-dimensional or less, and cognitively very distinct actions. For example, moving an object in 3-D space from point A to point B requires a minimum of three actions using the mouse: 1) move along one plane, 2) switch movement to second plane and 3) complete movement to desired position. Very often additional actions are required to effect small corrections.
The second type of device provides control in three input axes. This type of device, which can be called a three degree of freedom isometric (not moving) device, is fixed in position on the user's desk. The user, by pushing a control knob left/right, away/toward and up/down can enter three different coordinates. This device, because it is fixed in place, as say compared to a mouse, is a force sensitive device where the force applied by the user keeps the cursor moving and the amount of force controls the speed of the cursor movement. The problem with this arrangement is that the user must pay particular attention to the cursor, releasing his/her force on the control knob when the cursor is at the correct location, as opposed to simply moving the device and hence the cursor to the correct location.
The third type of device is a device with three degrees of freedom. This device is held in the hand and is freely moved about in three dimensions in a three dimensional electromagnetic field and the position and motion in three dimensions controls proportional movements of the cursor in three dimensions. This type of device can be extremely fatiguing on the user since the device has to be supported in the air by the user and is not practical for day in and day out input.
What is needed is a system that allows the ease of use and position control of a mouse but does not require the need for the separate actions to control the third dimension as in the mouse.